Cable power loss determination for virtual metrology

ABSTRACT

A method for modeling cable loss is described. The method includes receiving a measurement of reverse power and forward power at a radio frequency (RF) generator. The method further includes computing theoretical power delivered to a matching network as a difference between the forward power and the reverse power and calculating a ratio of the reverse power to the forward power to generate an RF power reflection ratio. The method further includes identifying a cable power attenuation fraction based on a frequency of the RF generator and calculating a cable power loss as a function of the RF power reflection ratio, the cable power attenuation fraction, and the theoretical power. The method includes calculating actual power to be delivered to the impedance matching network based on the theoretical power and the cable power loss and sending the calculated actual power to the RF generator to generate an RF signal.

CLAIM OF PRIORITY

The present patent application is a continuation of and claims priority,under 35 U.S.C. § 120, to U.S. patent application Ser. No. 14/152,791,filed on Jan. 10, 2014, and titled “Cable Power Loss Determination forVirtual Metrology”, now U.S. Pat. No. 9,594,105, which is incorporatedby reference herein in its entirety.

FIELD

The present embodiments relate to determination of cable power loss forvirtual metrology.

BACKGROUND

Plasma systems are used to supply power to a plasma chamber. The poweris generated by an RF generator and is supplied by the RF generator viaa matchbox to generate plasma within the plasma chamber.

Within the plasma chamber is a wafer, which is processed by the plasma.The wafer is etched, or deposited on, or cleaned with the plasma. Duringprocessing of the wafer, it is important to control the plasma toachieve accuracy in the processing and to increase wafer yield.

To measure properties of the power that is supplied and to measureproperties of the plasma, a sensor is connected to an input of thematchbox. However, use of the sensor is costly, time consuming, andprone to errors.

It is in this context that embodiments described in the presentdisclosure arise.

SUMMARY

Embodiments of the disclosure provide apparatus, methods and computerprograms for determining cable power loss using virtual metrology. Itshould be appreciated that the present embodiments can be implemented innumerous ways, e.g., a process, an apparatus, a system, a device, or amethod on a computer-readable medium. Several embodiments are describedbelow.

In some embodiments, instead of a sensor that is coupled to an input ofan impedance matching network, a processor is used to determine actualdelivered power at the input. A voltage and current probe measures acomplex voltage and current at an output of a radio frequency (RF)generator. The complex voltage and current is used to calculatetheoretical delivered power at the output of the RF generator. Theactual delivered power at the input of the impedance matching network isdetermined as a function of the theoretical delivered power, a cablepower attenuation fraction of an RF cable that connects the impedancematching network to the RF generator, and an RF power reflection ratio.The RF power reflection ratio is determined by the processor based onforward power that is measured at the output of the RF generator andreverse power that is measured at the output of the RF generator.

In various embodiments, a method for modeling cable loss is described.The method includes receiving a measurement of reverse power at a radiofrequency (RF) generator, which is coupled via an RF cable to animpedance matching network. The impedance matching network is coupledvia an RF transmission line to a plasma chamber. The RF generator has afrequency of operation. The method further includes receiving ameasurement of forward power at the RF generator, computing theoreticalpower delivered to the impedance matching network as a differencebetween the forward power and the reverse power, and calculating a ratioof the reverse power to the forward power to generate an RF powerreflection ratio. The method further includes identifying a cable powerattenuation fraction of the RF cable based on the frequency of operationof the RF generator, and calculating a cable power loss as a function ofthe RF power reflection ratio, the cable power attenuation fraction, andthe theoretical power. The method includes calculating actual power tobe delivered to the impedance matching network based on the theoreticalpower and the cable power loss and sending the calculated actual powerto the RF generator to generate an RF signal. The method is executed bya processor.

In several embodiments, a method includes receiving a measurement ofreverse power at an RF generator, which is coupled via an RF cable to animpedance matching network. The impedance matching network coupled viaan RF transmission line to a plasma chamber. The RF generator has afrequency of operation. The method further includes receiving ameasurement of forward power at the RF generator, computing theoreticalpower delivered to the impedance matching network as a differencebetween the forward power and the reverse power, and calculating a ratioof the of the reverse power to the forward power to generate an RF powerreflection ratio. The method includes identifying a cable powerattenuation fraction of the RF cable based on the frequency of operationof the RF generator and calculating a cable power loss as a function ofthe RF power reflection ratio, the cable power attenuation fraction, andthe theoretical delivered power. The method includes calculating actualpower to be delivered to the impedance matching network based on thetheoretical delivered power and the cable power loss, and determining anactual power at a node associated with a computer-generated model basedon the actual power delivered to the impedance matching network. Themethod is executed by a processor.

In some embodiments, a plasma system includes a radio frequency (RF)generator for supplying forward power. The RF generator has a frequencyof operation. The plasma system further includes an impedance matchingcircuit coupled to the RF generator for receiving the forward power andto generate a modified RF signal based on the forward power. The plasmasystem includes an RF cable coupling the RF generator to the impedancematching circuit to facilitate a transfer of the forward power to theimpedance matching circuit, and a plasma chamber coupled to theimpedance matching circuit via an RF transmission line. The plasmachamber is used for generating plasma based on the modified RF signal.The plasma system includes a sensor coupled to the RF generator tomeasure the forward power and to measure reverse power. The reversepower is reflected from the plasma towards the RF generator via the RFcable. The plasma system further includes a host system coupled to thesensor for receiving the measurement of the forward power and thereverse power. The host system is configured to compute theoreticalpower delivered to the impedance matching circuit as a differencebetween the forward power and the reverse power, calculate a ratio ofthe of the reverse power to the forward power to generate an RF powerreflection ratio, and identify a cable power attenuation fraction of theRF cable based on the frequency of operation of the RF generator. Thehost system is further configured to calculate a cable power loss as afunction of the RF power reflection ratio, the cable power attenuationfraction, and the theoretical delivered power. The host system isconfigured to calculate actual power to be delivered to the impedancematching circuit based on the theoretical delivered power and the cablepower loss and send the calculated actual power to the RF generator tocontrol the RF generator.

Some advantages of the above-described embodiments include using a cablepower attenuation fraction of an RF cable, an RF power reflection ratioof an output of an RF generator, and theoretical delivered power at theoutput of the RF generator to determine actual delivered power at aninput of an impedance matching network. There is no need to use a sensorat the input of the impedance matching network to measure actualdelivered power at the input. Use of the sensor takes time to connectthe sensor and to measure the actual delivered power at the input.Moreover, the sensor is costly and any measurements generated by thesensor are prone to errors.

Other aspects will become apparent from the following detaileddescription, taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments may best be understood by reference to the followingdescription taken in conjunction with the accompanying drawings.

FIG. 1 is a diagram of a plasma system for cable power lossdetermination, in accordance with some embodiments described in thepresent disclosure.

FIG. 2A is a diagram of a cable model, which is a computer-generatedmodel of a radio frequency (RF) cable of the plasma system of FIG. 1, inaccordance with various embodiments described in the present disclosure.

FIG. 2B is a diagram of another cable model, in accordance with severalembodiments described in the present disclosure.

FIG. 3 is a diagram used to illustrate that a cable power attenuationfraction associated with an attenuation of power by an RF cable isdependent upon a length of the RF cable and a frequency of operation ofan RF generator that is connected to the RF cable, in accordance withsome embodiments described in the present disclosure.

FIG. 4 is an embodiment of a graph to illustrate a relationship betweena cable power attenuation fraction of an RF cable and a frequency of anRF generator that is connected to the RF cable to provide an RF signalvia the RF cable, in accordance with various embodiments described inthe present disclosure.

FIG. 5 shows embodiments of graphs to illustrate a relationship betweenan error between a value of a variable that is generated using a modeledvalue of the variable without use of an equation and a measured value ofthe variable, in accordance with several embodiments described in thepresent disclosure.

FIG. 6 shows embodiments of graphs to illustrate a reduction in an errorin a variable when the equation is used to determine a cable power loss,in accordance with some embodiments described in the present disclosure.

FIG. 7 is a block diagram of an embodiment of a memory device that isused to illustrate use of actual delivered power at an output of an RFcable model to calculate an actual power at an output of a model node ofanother part of the plasma system, in accordance with variousembodiments described in the present disclosure.

FIG. 8 is a diagram of a host system, in accordance with severalembodiments described in the present disclosure.

DETAILED DESCRIPTION

The following embodiments describe systems and methods for cable powerloss determination using virtual metrology. It will be apparent that thepresent embodiments may be practiced without some or all of thesespecific details. In other instances, well known process operations havenot been described in detail in order not to unnecessarily obscure thepresent embodiments.

FIG. 1 is a diagram of an embodiment of a plasma system 100 for cablepower loss determination. The plasma system 100 includes an x megahertz(MHz) radio frequency (RF) generator, a y MHz RF generator, and a z MHzRF generator. Examples of x MHz include 2 MHz, 27 MHz, and 60 MHz.Examples of y MHz include 2 MHz, 27 MHz, and 60 MHz. Examples of z MHzinclude 2 MHz, 27 MHz, and 60 MHz.

In some embodiments, the x MHz is different than y MHz and z MHz, and yMHz is different than z MHz. For example, when x MHz is 2 MHz, y MHz is27 MHz and z MHz is 60 MHz.

In some embodiments, each RF generators includes a digital signalprocessor (DSP) and an RF supply. For example, the x MHz RF generatorincludes a DSP 160 and an RF supply 162. The DSP 160 is coupled to theRF supply 162 and to a host system 118. Similarly, the host system 118is coupled to a DSP (not shown) of the y MHz RF generator and to a DSP(not shown) of the z MHz RF generator. A DSP of an RF generator iscoupled to an RF supply of the RF generator.

Each RF generator includes a complex voltage and current sensor. Forexample, the x MHz RF generator includes a sensor 116 that is coupled toan RF cable 104A at an output 170 of the x MHz RF generator to measure acomplex voltage and current at the output. In various embodiments, acomplex voltage and current sensor that is used to calibrate the x, y,or z MHz RF generator at an output of the RF generator follows aNational Institute of Standards and Technology (NIST) standard. Forexample, the sensor 116 used to calibrate the x MHz RF generator is NISTtraceable. The NIST standard provides a degree of accuracy specified bythe NIST standard to a complex voltage and current sensor.

In some embodiments, a complex voltage and current includes a magnitudeof the current, a magnitude of the voltage, and a phase between thecurrent and the voltage. In some embodiments, a complex variable, e.g.,a complex impedance, complex power, etc., includes a magnitude of thevariable and a phase of the variable.

In some embodiments, the sensor 116 measures reverse power P_(rev) ofthe x MHz RF generator and forward power P_(fwd) of the x MHz RFgenerator. For example, the sensor 116 measures the reverse powerP_(rev) of the x MHz RF generator at the output 170 of the x MHz RFgenerator and measures the forward power P_(fwd) of the x MHz RFgenerator at the output 170. The forward power of an RF generator ispower of an RF signal supplied by the RF generator to an impedancematching network 102. The reverse power of an RF generator is powerreflected from the plasma chamber 166 via an RF transmission line 114,the impedance matching network 102, and a corresponding RF cable to theRF generator. For example, the reverse power of the x MHz RF generatoris power reflected by plasma formed within the plasma chamber 166 viathe RF transmission line 114, the impedance matching network 114, andthe RF cable 104A to the x MHz RF generator.

In some embodiments, reverse power is complex power and forward power iscomplex power.

In several embodiments, the impedance matching network 102 is a circuitof one or more inductors and/or one or more capacitors. Each component,e.g., inductor, capacitor, etc., of the impedance matching network 102is connected in series, or in parallel, or acts as a shunt, to anothercomponent of the impedance matching network 102.

In various embodiments, an RF cable includes an inner conductor that issurrounded by an insulation material, which is surrounded by an outerconductor, which is further surrounded by a jacket. In severalembodiments, the outer conductor is made of braided wire and the jacketis made of an insulator material. In some embodiments, an RF cable hasan internal impedance. In various embodiments, an RF cable has acharacteristic impedance, which is a function of an inductance and/or acapacitance of the RF cable.

The host system 118 includes one or more processors, e.g., a processor110, etc., and one or more memory devices. Examples of a processorinclude a central processing unit (CPU), a microprocessor, anapplication specific integrated circuit (ASIC), and a programmable logicdevice (PLD), etc. Examples of a memory device include a read-onlymemory (ROM), a random access memory (RAM), or a combination thereof.Other examples of a memory device include a flash memory, anon-transitory computer-readable storage medium, a redundant array ofstorage disks (RAID), a hard disk, etc.

The plasma system 100 further includes the impedance matching network102 that is coupled to the x, y, and z MHz RF generators. The impedancematching network 102 is coupled to the x MHz RF generator via the RFcable 104A, to the y MHz RF generator via another RF cable 104B, and tothe z MHz RF generator via an RF cable 104C.

In some embodiments, the impedance matching network 102 includes anetwork of RF electrical circuit elements, e.g., capacitors, inductors,etc., coupled with each other.

The impedance matching network 102 is coupled to the plasma chamber 112via the RF transmission line 114. In various embodiments, the RFtransmission line 114 includes a cylinder, e.g., a tunnel, etc., that isconnected to the impedance matching network 102. Within a hollow of thecylinder lies an insulator and an RF rod. The RF transmission line 114further includes an RF spoon, e.g., an RF strap, etc., that is coupledat one end to the RF rod of the cylinder. The RF spoon is coupled atanother end to an RF rod of a vertically placed cylinder and the RF rodis coupled to a chuck 164 of the plasma chamber 112.

The plasma chamber 112 includes the chuck 164, an upper electrode 166,and other parts (not shown), e.g., an upper dielectric ring surroundingthe upper electrode 166, an upper electrode extension surrounding theupper dielectric ring, a lower dielectric ring surrounding a lowerelectrode of the chuck 164, a lower electrode extension surrounding thelower dielectric ring, an upper plasma exclusion zone (PEZ) ring, alower PEZ ring, etc. The upper electrode 166 is located opposite to andfacing the chuck 164. A work piece 168 is supported on an upper surface171 of the chuck 164. Each of the lower electrode and the upperelectrode 166 is made of a metal, e.g., aluminum, alloy of aluminum,copper, etc. The chuck 164 may be an electrostatic chuck (ESC) or amagnetic chuck. The upper electrode 166 is coupled to a referencevoltage, e.g., a ground voltage, a zero voltage, a negative voltage,etc.

In some embodiments, the work piece 168 includes a semiconductor wafer.Various processes, e.g., chemical vapor deposition, cleaning,deposition, physical vapor deposition (PVD), chemical vapor deposition(CVD), plasma-enhanced CVD (PECVD), metal CVD, a high-density plasma CVD(HDP-CVD) function, a photoresist strip function, a photoresist surfacepreparation, ultraviolet thermal processing (UVTP), sputtering, etching,ion implantation, resist stripping, etc., are performed on the workpiece 168 during production. Integrated circuits, e.g., applicationspecific integrated circuit (ASIC), programmable logic device (PLD),etc. are developed on the semiconductor wafer and the integratedcircuits are used in a variety of electronic items, e.g., cell phones,tablets, smart phones, computers, laptops, networking equipment, etc. Invarious embodiments, the work piece 168 includes a substrate, one ormore layers, e.g., oxide layers, etc., on top of the substrate, andintegrated circuits on top of the substrate. In several embodiments, thework piece 168 includes a substrate, one or more layers, e.g., oxidelayers, etc., on top of the substrate, and integrated circuits on top ofthe layers. In various embodiments, the work piece 168 includes asubstrate and integrated circuits formed on top of the substrate.

In various embodiments, the upper electrode 166 includes one or more gasinlets, e.g., holes, etc., that are coupled to a central gas feed (notshown). The central gas feed receives one or more process gases from agas reservoir (not shown). An example of a process gas includes anoxygen-containing gas, such as O₂. Other examples of the process gasinclude a fluorine-containing gas, e.g., tetrafluoromethane (CF₄),sulfur hexafluoride (SF₆), hexafluoroethane (C₂F₆), etc.

The host system 118 sends control values, e.g., values of complex power,values of frequencies of operation, etc., to the x, y, and z MHz RFgenerators. For example, the processor 110 provides a value of complexpower and a value of a frequency of operation to the DSP 160 of the xMHz RF generator.

The DSPs of the x, y, and z MHz RF generators receive the control valuesand generate supply values, e.g., values of complex power, values offrequencies of operation, etc., based on the control values to provideto the RF supplies of the RF generators. For example, the DSP 160 of thex MHz RF generator generates a supply value of complex power and supplyvalue of a frequency of operation to provide to the RF supply 162 of thex MHz RF generator. In some embodiments, a supply value is the same as acontrol value. In various embodiments, a supply value is a drive valuethat is looked-up from a memory device of an RF generator by a DSP ofthe RF generator based on a control value.

The RF supplies of the x, y, and z RF generators generate an RF signalin response to receiving a supply value. For example, the RF supply 162generates an RF supply signal upon receiving a drive complex power valueand a drive operation frequency value from the DSP 160. Similarly, the yand z MHz RF generators generate RF signals.

The RF signals that are generated by the x, y, and z MHz RF generatorsare supplied via the RF cables that couple the generators to theimpedance matching network 102. For example, an RF signal that isgenerated by the x MHz RF generator is supplied via the RF cable 104A tothe impedance matching network 102.

Upon receiving the RF signals from the x, y, and z MHz RF generators,the impedance matching network 102 matches an impedance of a loadcoupled to the impedance matching network 102 with an impedance of asource coupled to the impedance matching network 102 to generate amodified RF signal. For example, the impedance matching network 102matches an impedance of an RF transmission line 114 and a plasma chamber112 with an impedance of the x MHz RF generator, the y MHz RF generator,the z MHz RF generator, the RF cable 104A, the RF cable 104B, and the RFcable 104C to generate the modified RF signal. As another example, theimpedance matching network 102 matches an impedance of any components ofthe plasma system 100 coupled to the impedance matching network 102 as aload with an impedance of any components of the plasma system 100coupled to the impedance matching network 102 as a source to generatethe modified RF signal. Examples of components coupled to the impedancematching network 102 as a load include the RF transmission line 114, theplasma chamber 112, and any other components, such as, for example, afilter, etc., coupled to the impedance matching network 102 on a side ofthe impedance matching network 102 on which the plasma chamber 112 islocated. Example of components coupled to the impedance matching network102 as a source include the x, y, and z RF generators, the RF cables104A, 104B, and 104C, and other components, e.g., a filter, etc.,coupled to a side of the impedance matching network 102 on which the RFgenerators are located.

The modified signal is sent by the impedance matching network 102 viathe RF transmission line 114 to the chuck 164. When the process gas issupplied between the upper electrode 166 and the chuck 164 and when themodified RF signal is supplied to the chuck 164, the process gas isignited to generate plasma within the plasma chamber 112.

The reverse and forward powers P_(rev) and P_(fwd) that are sensed bythe sensor 116 are received by the processor 110 via a cable 172A, suchas, for example, a cable that facilitates a parallel transfer of data, acable that facilitates a serial transfer of data, or a Universal SerialBus (USB) cable. Similarly, reverse and forward powers that are measuredby the sensors of the y and z MHz RF generators are received via cables172B and 172C by the processor 110.

The processor 110 computes theoretical power P_(deltheor), e.g.,P_(delin), etc., delivered by the x MHz RF generator to the impedancematching network 102 as a function, e.g., a difference, etc., betweenthe forward power P_(fwd) and the reverse power P_(rev). Similarly, theprocessor 110 calculates theoretical power delivered by the y and z MHzRF generators to the impedance matching network 102 as a function offorward power supplied by the y and z RF generators and reverse powerreflected towards the y and z MHz RF generators from the plasma chamber112.

In some embodiments, the sensor 116 measures the theoretical powerP_(deltheor) at the input 176 of the impedance matching network 102.

The processor 110 further calculates a ratio of the reverse powerP_(rev) to the forward power P_(fwd) to generate an RF power reflectionratio Γ² and further computes a magnitude |Γ²| of the RF powerreflection ratio. For example, the processor 110 performs a division ofthe reverse power P_(rev) to the forward power P_(fwd) to generate an RFpower reflection ratio Γ². As another example, the RF power reflectionratio is provided as:Γ² =P _(rev) /P _(fwd)  (1)

Similarly, the processor 110 calculates RF power reflection ratios fromforward and reverse powers received from the sensors of the y and z MHzRF generators.

Moreover, the processor 110 determines a cable power attenuationfraction A of the RF cable 104A based on the frequency of operation ofthe x MHz RF generator. For example, the processor 110 identifies thecable power attenuation fraction A of the RF cable 104A from a look-uptable that includes a list of frequencies of operation of a number of RFgenerators within a memory device of the host system 118 by looking-up acorresponding frequency of operation of the x MHz RF generator. Based onthe frequency of operation of the x MHz RF generator, the cable powerattenuation fraction A is identified. Similarly, the processor 110determines cable power attenuation fractions of the RF cables 104B and104C.

The processor 110 further calculates a cable power loss P_(delloss)associated with, e.g., incurred by, etc., the RF cable 104A as afunction of the RF power reflection ratio Γ² and the cable powerattenuation fraction A. For example, the cable power loss P_(delloss) isprovided as:

$\begin{matrix}{P_{delloss} = \left( {P_{deltheor}{A\left( \frac{1 + \Gamma^{2}}{1 - \Gamma^{2}} \right)}} \right)} & (2)\end{matrix}$

The cable power loss P_(delloss) is a product of the theoretical powerP_(deltheor), the cable power attenuation fraction A, and a term. Theterm includes a ratio of a sum of one and the RF power reflection ratioΓ² and a difference of one and the RF power reflection ratio Γ². In someembodiments, the cable power loss P_(delloss) is loss of delivered poweroccurring within the RF cable 104A. Similarly, the processor 110computes cable power losses associated with the RF cables 104B and 104C.

The processor 110 calculates actual power P_(delactual) to be deliveredto the impedance matching network 102 by the x MHz RF generator based onthe theoretical delivered power P_(deltheor) and the cable power lossP_(delloss). For example, the actual power P_(delactual) is computed asa difference between the delivered power P_(deltheor) and the cablepower loss P_(delloss) of the RF cable 104A. Similarly, the processor110 calculates actual powers to be delivered to the impedance matchingnetwork 102 by the y and z MHz RF generators.

In some embodiments, the processor 110 sends the calculated actual powerP_(delactual) via a cable 174A to the DSP 160 of the x MHz RF generator.Similarly, the processor 110 sends calculated actual powerscorresponding to the y and z MHz RF generators via cables 174 and 174Cto the DSPs of the y and z MHz RF generators. Examples of each cable174A, 174B, and 174C include a cable that facilitates a paralleltransfer of data, a cable that facilitates a serial transfer of data,and a USB cable.

The DSP 160 receives the calculated actual power P_(delactual) andretrieves, e.g., reads, etc., a drive actual power value correspondingto the actual power P_(delactual) and provides the drive actual powervalue to the RF supply 162. For example, the DSP 160 identifies, withina look-up table, stored within a memory device of the x MHz RF generatorthe drive actual power value corresponding to the calculated actualpower P_(delactual). As another example, the drive actual power value isthe same as the calculated actual power P_(delactual). Similarly, DSPsof the y and z MHz RF generators receive calculated actual power valuesfrom the processor 110 via the cables 174B and 174C and retrieve driveactual power values, which are provided to RF supplies of the y and zMHz RF generators.

The RF supply 162 includes a driver (not shown) and an amplifier (notshown), which is connected to the driver. The driver of the RF supply162 receives the drive actual power value from the DSP 160 and generatesan RF signal having the drive actual power value. The amplifier of theRF supply 162 amplifies, e.g., increases a magnitude of, etc., thegenerated RF signal and sends the amplified RF signal via the RF cable104A to the impedance matching network 102. In some embodiments, thereis no amplification performed and the magnitude of the amplified RFsignal is the same as that of the RF signal that is generated by thedriver of the RF supply 162. Similarly, amplified RF signals aregenerated by the RF supplies of the y and z MHz RF generators.

The impedance matching network 102 approximately matches an impedance ofa load with that of a source based on the amplified RF signal receivedfrom the RF supply 162 via the RF cable 104A and the amplified RFsignals received from RF supplies of the y and z MHz RF generators togenerate a modified RF signal, and provides the modified RF signal viathe RF transmission line 114 to the chuck 164 to generate or modifyplasma within the plasma chamber 112. For example, the impedancematching network 102 matches an impedance of a load to be within athreshold of an impedance of a source. As another example, the impedancematching network 102 substantially matches an impedance of a load withan impedance of a source.

In a manner similar to that described above, the impedance matchingnetwork 102 generates a modified RF signal based on the RF signalsreceived from the x, y, and z MHz RF generators and provides themodified RF signal via the RF transmission line 114 to the plasmachamber 112 to generate or modify plasma within the plasma chamber 112.

It should be noted that in some embodiments, there is no need to use asensor 120 at an input 176 of the impedance matching network 102 whenthe processor 110 is used to generate the calculated actual powerP_(delactual). The sensor 120 is used to measure forward power andreverse power at the input 176, which is further used to calculateactual power P_(delout) that is delivered to the input 176 via the RFcable 104A. The sensor 120 is costly and has inaccuracies. Theinaccuracies result in generation of an imprecise actual power value bythe sensor 120. Moreover, coupling of the sensor 120 to the input 176and decoupling of the sensor 120 from the input 176 is time consuming.The input 176 is connected to the output 170 of the x MHz RF generator.

In some embodiments, the plasma system 100 includes any number of RFgenerators. For example, the plasma system 100 includes one or two orfour RF generators.

It should further be noted that in some embodiments, the forward powersassociated with the x, y, and z RF generators, the reverse powersassociated with the RF generators, the theoretical powers associatedwith the RF generators, the RF power reflection ratios associated withthe RF generators, magnitudes of RF power reflection ratios associatedwith the RF generators, the cable power attenuation fractions associatedwith the RF cables 104A, 104B, and 104C, and the cable power lossesassociated with the RF cables, and actual powers delivered to theimpedance matching network 102 by the RF generators are stored withinthe memory device of the host system 118.

In various embodiments, the operations described herein as beingperformed by the processor 110 are performed by a number of processors,e.g., two or more processors.

In some embodiments, the equation (2) is derived. The derivation isperformed by the processor 110 and is described as follows:P _(deltheor) =P _(fwd)[1−Γ²]  (3)

P_(fwd) (1−A) is theoretical power that reaches the impedance matchingnetwork 102 and RP_(fwd) (1−A) is theoretical power reflected at theimpedance matching network 102, where R is an actual power reflectionfraction at the impedance matching network 102. (1−R)P_(fwd) (1−A) istheoretical power transmitted, e.g., delivered, etc., to the impedancematching network 102. Theoretical power that returns to an RF generatorthat is coupled to an RF cable having the cable power attenuationfraction A is P_(rev)=RP_(fwd)(1−A)²=Γ²P_(fwd)=>Γ²=R(1−A)². Power to beactually delivered to the impedance matching network 102 is:

$\begin{matrix}\begin{matrix}{{\left( {1 - R} \right){P_{fwd}\left( {1 - A} \right)}} = {{P_{fwd}\left( {1 - \frac{\Gamma^{2}}{\left( {1 - A} \right)^{2}}} \right)}\left( {1 - A} \right)}} \\{= {P_{fwd}\left( {1 - A - \frac{\Gamma^{2}}{1 - A}} \right)}} \\{\approx {P_{fwd}\left( {1 - A - {\Gamma^{2}\left( {1 + A} \right)}} \right)}} \\{= {{P_{fwd}\left( {1 - \Gamma^{2}} \right)} - {P_{fwd}{A\left( {1 + \Gamma^{2}} \right)}}}} \\{= {P_{deltheor} - {P_{deltheor}A\frac{1 + \Gamma^{2}}{1 - \Gamma^{2}}}}}\end{matrix} & (4)\end{matrix}$

FIG. 2A is a diagram of an embodiment of a cable model 180, which is acomputer-generated model of an RF cable, e.g., the RF cable 104A, or104B, or 104C (FIG. 1), etc. The cable model 180 is generated by theprocessor 110 (FIG. 1) to represent a cable power loss of an RF cable.For example, the cable model 180 represents the cable power lossP_(delloss), which is a loss of delivered power that is attributed bythe processor 110 to the RF cable 104A. Power that is delivered at anoutput 184 of the cable model 180 is a function of a power delivered atan input 182 of the cable model 180 and a cable power loss attributed toan RF cable that is represented by the cable model 180. For example,power P_(delout) that is delivered at an output 184 of the cable model180 is a difference between the power delivered P_(delin) at an input182 of the cable model 180 and the cable power loss P_(delloss) that isattributed to the RF cable 104A.

A cable power loss of an RF cable is a function of cable powerattenuation fraction of the RF cable and a RF power reflection ratioassociated with the RF cable, e.g., the RF cable 104A, or 104B, or 104C(FIG. 1), etc. For example, the cable power loss P_(delloss) attributedby the processor 110 to the RF cable 104A is dependent upon the cablepower attenuation fraction A of the RF cable 104A and the RF powerreflection ratio Γ² of the RF cable 104A.

FIG. 2B is a diagram of an embodiment of another cable model 182, whichis a computer-generated model of an RF cable. The cable model 182 is anexample of the cable model 180 (FIG. 2A). Cable power loss that isattributed by the processor 110 to an RF cable is a function of powerdelivered to an input 188 of the cable model 186, cable powerattenuation fraction of the RF cable, and RF power reflection ratioassociated with the RF cable. For example, the cable power lossP_(delloss) is provided by equation (2) above. Power delivered at anoutput 190 of the cable model is a function of the power delivered atthe input 188 and the cable power loss associated with the cable model186. For example, the power P_(delout) delivered at the output 190 iscalculated as a difference between the power P_(delin) delivered at theinput 188 and the cable power loss P_(delloss) of the RF cable 104A.

It should be noted that the input 188 is an example of the input 182(FIG. 2A) and the output 190 is an example of the output 184 (FIG. 2A).

FIG. 3 is a diagram used to illustrate that a cable power attenuationfraction associated with attenuation of power by an RF cable isdependent upon a length of the RF cable and a frequency of operation ofan RF generator that is connected to the RF cable. For example, theprocessor 110 (FIG. 1) determines the cable power attenuation fraction Aof the RF cable 104A (FIG. 1) based on a length L of the RF cable 104Aand a frequency of operation of the x MHz RF generator that is connectedto the RF cable 104A and that supplies an RF signal via the RF cable104A to the impedance matching network 102 (FIG. 1).

FIG. 4 is an embodiment of a graph 191 that is shown to illustrate arelationship between a cable power attenuation fraction of an RF cableand a frequency of an RF generator that is connected to the RF cable toprovide an RF signal via the RF cable and the impedance matching network102 (FIG. 1) to the plasma chamber 112 (FIG. 1). The graph 191 includesa plot of a cable power attenuation fraction, measured in decibels per100 feet, of an RF cable, versus a square root of a frequency ofoperation of an RF generator that is coupled to the RF cable. The cablepower attenuation fraction is plotted on a y-axis and the square root offrequency of operation is plotted on an x-axis.

The graph 191 includes a plot 192 of an RF cable 1 and a plot 194 ofanother RF cable 2. The plot 194 is linear and the plot 192 is a plot ofa polynomial. In some embodiments, the plot 192 is an exponentialfunction.

It should be noted that a cable power attenuation fraction of an RFcable increases with a frequency of operation of an RF generator that iscoupled to the RF cable.

In some embodiments, instead of every 100 feet of an RF cable, a cablepower attenuation fraction is measured every 10 feet or 1 feet or 2 feetor any other number of feet of the RF cable. In various embodiments,instead of feet, any other unit of length, e.g., meters, or centimeters,or inches, etc., is used.

In various embodiments, a cable power attenuation fraction of an RFcable that is coupled to an RF generator is extrapolated to a frequencyof operation of the RF generator by the processor 110 based on highfrequencies, e.g., frequencies above 100 MHz, frequencies above 90 MHz,frequencies above 60 MHz etc., and based on cable power attenuationfractions corresponding to the frequencies.

FIG. 5 shows embodiments of graphs 196 and 198 to illustrate arelationship between an error between a value of a variable, e.g.,voltage, current, etc., that is generated using a modeled value of thevariable without use of the equation (2) and a measured value of thevariable. For example, the graph 196 plots a percentage error in amodeled voltage that is generated an input of a computer-generated modelof an impedance matching network versus a voltage that is measured atthe input. Also, in this example, the percentage error is plotted on ay-axis and the measured voltage in plotted on an x-axis. In thisexample, the measured voltage is sensed using a voltage sensor at anoutput of an RF cable that is represented by a computer-generated modeland that is coupled to the impedance matching network. Further, in thisexample, the modeled voltage is generated by propagating a value of avoltage at an input of the computer-generated model of the RF cable viathe computer-generated model of the RF cable. To illustrate, a modeledvoltage is propagated by generating a directional sum of the voltage andof modeled voltages of one or more elements of the computer-generatedmodel of the RF cable. In this illustration, the elements includecapacitors, or inductors, or a combination thereof. The elements of thecomputer-generated model of the RF cable have the same or similarcharacteristics as that of components of an RF cable that is representedby the computer-generated model. For example, when the RF cable has acapacitance of M and an inductance of N, the elements have a capacitanceof M and an inductance of N. As another example, when the componentsinclude a real capacitor coupled in series with a real inductor, theelements include a modeled capacitor in series with a modeled inductor.As yet another example, when the components include a real capacitorcoupled in parallel with a real inductor, the elements include a modeledcapacitor in parallel with a modeled inductor. It should be notedexamples of the elements of a computer-generated model include one ormore capacitors, one or more inductors, or a combination thereof.

Similarly, the graph 198 plots a percentage error in a modeled currentthat is generated at an input of a computer-generated model of animpedance matching network versus a current that is measured at theinput. The percentage error in current is plotted on a y-axis and themeasured current in plotted on an x-axis.

As shown in graphs 196 and 198, percentage errors are close to and aboveone percent.

In some embodiments, an input of a computer-generated model of animpedance matching network is coupled to an output of acomputer-generated model of an RF cable that is connected to theimpedance matching network.

FIG. 6 shows embodiments of graphs 202 and 204 to illustrate a reductionin error in a variable when equation (2) is used to determine a cablepower loss. The graph 202 plots a percentage error in a modeled voltagethat is determined based on a cable power loss calculated using equation(2) versus a measured voltage, which is voltage measured by coupling avoltage sensor at an input of an impedance matching network that isrepresented by a computer-generated model. The computed-generated modelof the impedance matching network has the modeled voltage at its input.The modeled voltage is generated from the cable power loss by theprocessor 110 (FIG. 1). The percentage error in the modeled voltage isplotted on a y-axis and the measured voltage is plotted on an x-axis.

Similarly, the graph 204 plots a percentage error in a modeled currentthat is determined from cable power loss of equation (2) versus ameasured current, which is current measured by coupling a current sensorat the input of the impedance matching network that is represented bythe computer-generated model of the impedance matching network.

It should be noted that percentage errors illustrated in FIG. 6 are lessthan the percentage errors illustrated in FIG. 5.

FIG. 7 is a block diagram of an embodiment of a memory device 122 thatis used to illustrate use of the actual delivered power P_(delactual) tocalculate an actual delivered power at an output of a model node. Thememory device 122 is a part of the host system 118. The memory device122 includes an impedance matching model 150, an RF transmission model152, and a chuck model 154.

The impedance matching model 150 is coupled to the model 180 (FIG. 2) toreceive the actual power P_(delactual) from an output of the model 180.The RF transmission model 152 is coupled to the impedance matching model150 at a model node O1, which is a node at an output of the impedancematching model 150 and at an input of the RF transmission model 152.

Moreover, the chuck model 154 is coupled to the RF transmission model152 at a model node O2, which is a node at an output of the RFtransmission model 152 and at an input of the chuck model 154. Also, thechuck model 54 has a model node O3.

In some embodiments, a model has similar characteristics as that of acorresponding part of the plasma system 100 (FIG. 1). For example, theimpedance matching model 150 has similar characteristics, e.g.,capacitances, inductances, resistances, complex power, complex voltageand currents, etc., as that of the impedance matching network 102. As anexample, the impedance matching model 150 has the same number ofcapacitors and/or inductors and/or resistors as that within theimpedance matching network 102, and the capacitors and/or inductorsand/or resistors are connected with each other in the same manner, e.g.,serial, parallel, etc. as that within the impedance matching network102. To provide an illustration, when the impedance matching network 102includes a capacitor coupled in series with an inductor, the impedancematching model 150 also includes the capacitor coupled in series withthe inductor.

As another example, the impedance matching network 102 includes one ormore electrical circuit components and the impedance matching model 150includes a design, e.g., a computer-generated model, of the impedancematching network 102. The computer-generated model may be generated bythe processor 110 based upon input signals received from a user via aninput hardware unit. The input signals include signals regarding whichelectrical circuit components, e.g., capacitors, inductors, resistors,etc., to include in a model and a manner, e.g., series, parallel, etc.,of coupling the electrical circuit components with each other. Asanother example, the impedance matching network 102 includes hardwareelectrical circuit components and hardware connections between theelectrical circuit components and the impedance matching model 150includes software representations of the hardware electrical circuitcomponents and of the hardware connections. As yet another example, theimpedance matching model 150 is designed using a software program andthe impedance matching network 102 is made on a printed circuit board.

As used herein, in some embodiments, electrical circuit componentsinclude resistors, capacitors, inductors, connections between theresistors, connections between the inductors, connections between thecapacitors, and/or connections between a combination of the resistors,inductors, and capacitors. Examples of connections between resistors,inductors, and/or capacitors include one or more conductors.

Similarly, the RF transmission model 152 and the RF transmission line114 have similar characteristics. For example, the RF transmission model152 has the same number of capacitors and/or inductors as that withinthe RF transmission line 114, and the capacitors and/or inductors areconnected with each other in the same manner, e.g., serial, parallel,etc. as that within the RF transmission line 114. To further illustrate,when the RF transmission line 114 includes a capacitor coupled inparallel with an inductor, the RF transmission model 152 also includesthe capacitor coupled in parallel with the inductor. As yet anotherexample, the RF transmission line 114 includes one or more electricalcircuit components and the RF transmission model 152 includes a design,e.g., a computer-generated model, of the RF transmission line 114.

Similarly, the chuck model 154 and the chuck 164 have similarcharacteristics. As an example, an inductance of the chuck model 154 isthe same as an inductance of the chuck 164. As another example, aresistance of the chuck model 154 is the same as a resistance of thechuck 164. As another example, the chuck model 154 is acomputer-generated model of the chuck 164.

The impedance matching model 150, the RF transmission model 152, and thechuck model 154 are generated by the processor 110.

The actual power P_(delactual) is propagated via the impedance matchingmodel 150 to the model node O1. For example, a directional sum of theactual power P_(delactual) and power values of delivered powerassociated with electrical circuit components of the impedance matchingmodel 150 is calculated to generate an actual delivered power at themodel node O1. Moreover, in some embodiments, the actual delivered powerat the model node O1 is propagated via electrical circuit components ofthe RF transmission model 152 to generate actual delivered power at themodel node O2. Also, in various embodiments, the actual delivered powerat the model node O2 is propagated via electrical circuit components ofthe chuck model 154 to generate an actual delivered power at the modelnode O3. For example, a directional sum of the actual delivered power atthe model node O2 and of actual delivered power of electrical circuitcomponents of the chuck model 154 is calculated to generate an actualdelivered power at the output node O3.

In various embodiments, the actual power P_(delactual) is propagated viaa portion of the impedance matching model 150 to generate actualdelivered power at an intermediate model node within the impedancematching model 150. The intermediate model node is between electricalcircuit components of the impedance matching model 150 at one side ofthe intermediate model node and electrical circuit components of theimpedance matching model 150 at another side of the intermediate modelnode.

Similarly, in some embodiments, the actual delivered power at the modelnode O1 is propagated via a portion of the RF transmission model 152 togenerate actual delivered power at an intermediate model node within theRF transmission model 152. The intermediate model node of the RFtransmission model 152 is between electrical circuit components of theRF transmission model 152 at one side of the intermediate model node andelectrical circuit components of the RF transmission model 152 atanother side of the intermediate model node.

Moreover, in various embodiments, the actual delivered power at themodel node O2 is propagated via a portion of the chuck model 154 togenerate actual delivered power at an intermediate model node within thechuck model 154. The intermediate model node of the chuck model 154 isbetween electrical circuit components of the chuck model 154 at one sideof the intermediate model node and electrical circuit components of thechuck model 154 at another side of the intermediate model node.

In some embodiments, the actual power P_(delactual), the actual power atthe model node O1, the actual power at the model node O2, and/or theactual power at the model node O3 is sent by the processor 110 to one ormore of the x, y, and z MHz RF generators to control RF signals that aregenerated by the one or more of the x, y, and z MHz RF generators tocontrol plasma within the plasma chamber 112. For example, the processor110 identifies that the actual power P_(delactual) exceeds a threshold.The processor 110 sends a signal to the DSP 160 of the x MHz RFgenerator to change power of an RF signal supplied by the RF supply 162.The RF signal with the changed amount of power is sent via the RF cable104A (FIG. 1), the impedance matching network 102, and the RFtransmission line 114 (FIG. 1) to the chuck 164 to modify properties ofplasma within the plasma chamber 112 to achieve the threshold.

In some embodiments, any functions described herein as performed by theprocessor 110 are performed by a processor of an RF generator or by acombination of the processor 110 and the processor of the RF generator.

FIG. 8 is a diagram of an embodiment of the host system 118. The hostsystem 118 includes the processor 110, a memory device 122, an inputdevice 220, an output device 222, an input/output (I/O) interface 270,an I/O interface 272, a network interface controller (NIC) 274, and abus 275. The processor 110, the memory device 122, the input device 220,the output device 222, the I/O interface 270, the I/O interface 272, andthe NIC 274 are coupled with each other via the bus 275. Examples of theinput device 220 include a mouse, a keyboard, a stylus, etc. Examples ofthe output device 222 include a display, a speaker, or a combinationthereof. The display may be a liquid crystal display, a light emittingdiode display, a cathode ray tube, a plasma display, etc. Examples ofthe NIC 274 include a network interface card, a network adapter, etc.

Examples of an I/O interface include an interface that providescompatibility between pieces of hardware coupled to the interface. Forexample, the I/O interface 270 converts a signal received from the inputdevice 220 into a form, amplitude, and/or speed compatible with the bus275. As another example, the I/O interface 272 converts a signalreceived from the bus 275 into a form, amplitude, and/or speedcompatible with the output device 222.

It is further noted that although the above-described operations aredescribed with reference to a parallel plate plasma chamber, e.g., acapacitively coupled plasma chamber, etc., in some embodiments, theabove-described operations apply to other types of plasma chambers,e.g., a plasma chamber of an inductively coupled plasma (ICP) reactor,or of a transformer coupled plasma (TCP) reactor, conductor tools, or ofan electron-cyclotron resonance (ECR) reactor, etc. For example, the xMHz RF generator, the y MHz RF generator, and the z MHz RF generator arecoupled to an inductor within a plasma chamber of the ICP reactor.

It is also noted that although the operations above are described asbeing performed by the processor 110, in some embodiments, theoperations may be performed by one or more processors of the host system118, or by multiple processors of multiple host systems, or by multipleprocessors of RF generators.

It should be noted that although the above-described embodiments relateto providing an RF signal to the lower electrode of a chuck of a plasmachamber, and grounding an upper electrode of the plasma chamber, inseveral embodiments, the RF signal is provided to the upper electrodewhile the lower electrode is grounded.

Embodiments described herein may be practiced with various computersystem configurations including hand-held hardware units, microprocessorsystems, microprocessor-based or programmable consumer electronics,minicomputers, mainframe computers and the like. The embodiments canalso be practiced in distributed computing environments where tasks areperformed by remote processing hardware units that are linked through anetwork.

With the above embodiments in mind, it should be understood that theembodiments can employ various computer-implemented operations involvingdata stored in computer systems. These operations are those requiringphysical manipulation of physical quantities. Any of the operationsdescribed herein that form part of the embodiments are useful machineoperations. The embodiments also relates to a hardware unit or anapparatus for performing these operations. The apparatus may bespecially constructed for a special purpose computer. When defined as aspecial purpose computer, the computer can also perform otherprocessing, program execution or routines that are not part of thespecial purpose, while still being capable of operating for the specialpurpose. In some embodiments, the operations may be processed by acomputer selectively activated or configured by one or more computerprograms stored in the computer memory, cache, or obtained over anetwork. When data is obtained over a network, the data may be processedby other computers on the network, e.g., a cloud of computing resources.

One or more embodiments can also be fabricated as computer-readable codeon a non-transitory computer-readable medium. In some embodiments, thenon-transitory computer-readable medium is a memory device that canstore data, which can be thereafter be read by a computer system.Examples of the non-transitory computer-readable medium include harddrives, network attached storage (NAS), ROM, RAM, compact disc-ROMs(CD-ROMs), CD-recordables (CD-Rs), CD-rewritables (CD-RWs), magnetictapes and other optical and non-optical data storage hardware units. Thenon-transitory computer-readable medium can include computer-readabletangible medium distributed over a network-coupled computer system sothat the computer-readable code is stored and executed in a distributedfashion.

Although the method operations above were described in a specific order,it should be understood that other housekeeping operations may beperformed in between operations, or operations may be adjusted so thatthey occur at slightly different times, or may be distributed in asystem which allows the occurrence of the processing operations atvarious intervals associated with the processing, as long as theprocessing of the overlay operations are performed in the desired way.

One or more features from any embodiment may be combined with one ormore features of any other embodiment without departing from the scopedescribed in various embodiments described in the present disclosure.

Although the foregoing embodiments have been described in some detailfor purposes of clarity of understanding, it will be apparent thatcertain changes and modifications can be practiced within the scope ofthe appended claims. Accordingly, the present embodiments are to beconsidered as illustrative and not restrictive, and the embodiments arenot to be limited to the details given herein, but may be modifiedwithin the scope and equivalents of the appended claims.

The invention claimed is:
 1. A method for using a computer-generatedmodel to determine power at an output of a radio frequency (RF) cable,comprising: receiving a measurement of power at an output of an RFgenerator from a sensor located within the RF generator, wherein saidreceiving the measurement of power is performed when the RF generator iscoupled via the RF cable to an impedance matching network and theimpedance matching network is coupled via an RF transmission line to aplasma chamber; generating, by a computer, a computer model of the RFcable, wherein the computer model of the RF cable has an input and anoutput, wherein the measurement is received at the input of the computermodel; propagating the power measured at the output of the RF generatorfrom the input of the computer model via the computer model to theoutput of the computer model to determine power at the output of thecomputer model; and controlling power supplied by the RF generator basedon the power at the output of the computer model.
 2. The method of claim1, wherein the power is measured by a sensor that follows a NationalInstitute of Standards and Technology (NIST) standard.
 3. The method ofclaim 1, wherein the computer model is generated from a cable powerattenuation fraction of the RF cable and an RF power reflection ratio,wherein the cable power attenuation fraction is generated from a lengthof the RF cable and a frequency of operation of the RF generator,wherein the RF power reflection ratio is generated from power that isreflected towards the RF generator and power that is supplied by the RFgenerator.
 4. The method of claim 3, wherein propagating the powermeasured at the output of the RF generator comprises computing the powerat the output of the computer model based on the power measured at theoutput of the RF generator, the cable power attenuation fraction, andthe RF power reflection ratio.
 5. The method of claim 1, wherein saidcontrolling the RF generator comprises sending a control signal to theRF generator to change an amount of the power generated and supplied bythe RF generator.
 6. A system for using a computer-generated model todetermine power at an output of a radio frequency (RF) cable,comprising: an RF generator having an output that is coupled to asensor, wherein the sensor is located within the RF generator; an RFcable coupled to the output of the RF generator; an impedance matchingnetwork coupled to the RF cable; an RF transmission line coupled to theimpedance matching network; a plasma chamber coupled to the RFtransmission line; and a host computer system coupled to the sensor,wherein the host computer system is configured to: receive a measurementof power at the output of the RF generator; generate a computer model ofthe RF cable, wherein the computer model of the RF cable has an inputand an output, wherein the measurement is received at the input of thecomputer model; propagate the power measured at the output of the RFgenerator from the input of the computer model via the computer model tothe output of the computer model to determine power at the output of thecomputer model; and control power that is supplied by the RF generatorbased on the power at the output of the computer model.
 7. The system ofclaim 6, wherein the sensor follows a National Institute of Standardsand Technology (NIST) standard.
 8. The system of claim 6, wherein thecomputer model is generated from a cable power attenuation fraction ofthe RF cable and an RF power reflection ratio, wherein the cable powerattenuation fraction is generated from a length of the RF cable and afrequency of operation of the RF generator, wherein the RF powerreflection ratio is generated from power that is reflected towards theRF generator and power that is supplied by the RF generator.
 9. Thesystem of claim 8, wherein the host computer system is configured tocompute the power at the output of the computer model based on the powermeasured at the output of the RF generator, the cable power attenuationfraction, and the RF power reflection ratio.
 10. The system of claim 6,wherein the host computer system is configured to send a control signalto the RF generator to change an amount of the power generated andsupplied by the RF generator.
 11. A non-transitory computer readablemedium storing a program causing a computer to execute a methodcomprising: receiving a measurement of power at an output of a radiofrequency (RF) generator from a sensor located within the RF generator,wherein said receiving the measurement of power is performed when the RFgenerator is coupled via an RF cable to an impedance matching networkand the impedance matching network is coupled via an RF transmissionline to a plasma chamber; generating a computer model of the RF cable,wherein the computer model of the RF cable has an input and an output,wherein the measurement is received at the input of the computer model;propagating the power measured at the output of the RF generator fromthe input of the computer model via the computer model to the output ofthe computer model to determine power at the output of the computermodel; and controlling power supplied by the RF generator based on thepower at the output of the computer model.
 12. The non-transitorycomputer readable medium of claim 11, wherein the measurement is made bya sensor that follows a National Institute of Standards and Technology(NIST) standard.
 13. The non-transitory computer readable medium ofclaim 11, wherein the computer model is generated from a cable powerattenuation fraction of the RF cable and an RF power reflection ratio,wherein the cable power attenuation fraction is generated from a lengthof the RF cable and a frequency of operation of the RF generator,wherein the RF power reflection ratio is generated from power that isreflected towards the RF generator and power that is supplied by the RFgenerator.
 14. The non-transitory computer readable medium of claim 13,wherein propagating the power measured at the output of the RF generatorcomprises computing the power at the output of the computer model basedon the power measured at the output of the RF generator, the cable powerattenuation fraction, and the RF power reflection ratio.
 15. Thenon-transitory computer readable medium of claim 11, wherein the methodfurther comprises controlling the RF generator based on the power at theoutput of the computer model, wherein said controlling the RF generatorcomprises sending a control signal to the RF generator to change anamount of the power generated and supplied by the RF generator.